Electric cartridge fuses



Oct. 29, 1957 .1. H. WATKISS 2,811,609

ELECTRIC CARTRIDGE FUSES Filed July 28, 1955 Inventor James H. Wq m s Attorney United States Patent C ice 2,811,609 ELECTRIC CARTRIDGE FUSES James Herbert Watkiss, Clieadle Heath, Stockport, England Application Jul 28, 1955, Serial No. 524,928 4 claims. (Cl. 200-133) This invention concerns electric cartridge fuses.

Cartridge fuses normally consists of a base in the form of a rectangular box, open at the top and a holder adapted to carry a fuse cartridge and by which the latter is introduced through the open top to contacts within the base. These contacts are usually resilient contacts each of U form. The base of the U is arcuate and the limbs, which extend towards the open top of the base firstly converge together to form a neck and then diverge before termination. Each contact is suitably anchored in the base.

The shape of the contacts just described enables the end caps of the fuse cartridge to be guided into the contacts by the initially diverging limbs and then by the exertion of sufiicient force to be snapped through the neck which then springs back to its normal position to hold the end caps within the arcuate part of the contact.

The fuse holder is normally adapted to carry the fuse cartridge by its reduced diameter central portion between the end caps.

The resilient contacts perform two functions. Their resiliency has to be such that they ensure firstly good electrical contact between themselves and the fuse cartridge end caps and, secondly, that the fuse cartridge is retained i nits operative position in spite of any normal vibration or shock.

In theory, the maximum pressure is exerted by the resilient contacts during passage of the fuse cartridge end caps through the restricted necks and therefore the pressure that can be exerted on the caps, in the operative position, with the necks returned to the normal position, is something less than the maximum. It will be seen therefore that a compromise must be made, by shaping of the resilient contacts so as to obtain suitable retaining power of the necks and contact pressure on the fuse cartridge end caps, both of which will be less than the maximum possible value.

It has hitherto been usual for the fuse holder to be screwed or otherwise fastened to the base when the fuse cartridge is in position and, of course, this renders the fuse cartridge less readily accessible and increases the time necessary to effect replacement. It does not, however, improve in any way the contact pressure of the spring contacts with the fuse cartridge end caps, and the fuse cartridge is still affected by certain vibrations.

The object of the present invention is to provide a fuse consisting of a base with U-shaped spring contacts of the type described and a contactless fuse cartridge holder in which, after introduction of the fuse cartridge to the contacts the latter are caused firmly to grip the fuse cartridge end caps, so as to improve contact pressure on the fuse cartridge and lock the fuse cartridge and the holder in position.

According to the present invention a cartridge fuse of the type having a box-like base with U-shaped spring contacts of the type described which receive laterally the end caps of a fuse cartridge held in a contactless holder of insulating material, is characterised in that the fuse holder locates the fuse cartridge laterally, whilst being 2,811,609 Patented Oct. 29, 1957 slidable in a longitudinal direction from a defined position in relation to the fuse cartridge whereby, in said defined position the fuse cartridge end caps may be introduced into the spring contacts in the base, and then the holder slidably moved relatively to the base, during Which movement the fuse cartridge remains substantially stationary in the contacts, and cam surfaces on said holder are effective firmly to close the spring contacts over the fuse cartridge end caps and thereby prevent lateral withdrawal of the fuse cartridge from the contacts and lateral separation of the holder from the base.

The invention will be described further, by way of example, with reference to the accompanying drawings in which: N

Fig. 1 is a sectional elevation of a fuse base for a fuse in accordance with the invention,

Fig. 2 is an end elevation corresponding to Fig. 1,

Fig. 3 is a plan view corresponding to Fig. 1,

Fig. 4 is an elevation of a fuse holder for a fuse constructed in accordance with the invention,

Fig. 5 is an end elevation corresponding to Fig. 4,

Fig. 6 is a plan view corresponding to Fig. 4,

Fig. 7 is a diagrammatic view in end elevation showing the relative positions of fuse base and holder at one stage of assembly,

Fig. 8 is an isometric view of an alternative form of spring contact for the fuse base,

Fig. 9 is an elevation of a second form of fuse holder, Fig. 10 is an end elevation corresponding to Fig. 9, and

Fig. 11 is a plan view corresponding to Fig. 9.

Referring to Figs. 1, 2 and 3, the fuse base 11 is of insulating material and in the form of a rectangular box and anchored at either end within the base is a copper spring contact 12. Each contact 12 rests in a seat 13 therefor and at each side has a projection 14 engageable with a notch 15 in the corresponding side wall of the base 11. Each contact 12 is also provided with a tail 16 which extends rearwardly of the base 11 through an aperture 17 therein, and serves for the attachment thereto of an electrical conductor (not shown).

The base 11 is provided with a further aperture 18 so that it may be attached by means of a screw, or the like, to its location which may be, for instance, a switch board.

Each contact 12 is of generally U-shape, the bottom thereof being of arcuate form and the limbs then converging to form a neck above the arcuate portion before diverging towards their termination.

Referring now to Figs. 4, 5 and 6, the fuse holder 19 is also of insulating material and may conveniently be a one-piece moulding, as also may be the fuse base of Figs. 1 to 3. Above one face of the holder 19 projects a stirrup 2 of inverted U-shape, the arcuate portion of which is of a radius substantially equal to that of the small diameter central portion of the fuse cartridge which the holder 19 is to carry.

That part of the holder 19 immediately beneath the strirup 20 is apertured and the remaining parts of that face of the holder 19 from which the stirrup 2i) extends are provided with a number of projections. From one end of the face extend for a short distance a pair of parallel projections 21, 21, the adjacent longitudinal faces of which are intended to act as cam surfaces and diverge one from the other as they approach the stirrup 20. These projections 21, 21, are followed by a single projection 22 centrally of the holder 19 which terminates at the transverse edge of an aperture 23 beneath the stirrup 20 and the top surface of which is chamfered away as it approaches this edge. From the other side of the stirrup 21 extend two projections 24, 24, in line with the first mentioned pair of projections 21, 21, and the adjacent longitudinal faces of which are similarly divergent as they approach the transverse edge of the holder 19. The projections 24, 24, terminate before reaching this edge. From this edge extends towards the stirrup 20, a projection 25centrally of the holder 19 and terminating with a chamfered end short of the other transverse edge of the aperture 23 beneath the stirrup 20.

The distance between the upper faces of the two projections 22, 25, lying centrally of the holder and the arcuate portion of the stirrup 20, is such that when the fuse cartridge 26 (shown chain dotted in Fig. 4) is introduced beneath the stirrup obliquely and passed therethrough with a tilting motion until its end caps 26a rest on these projections, the fuse cartridge is positively located in all lateral directions. The stirrup 20 is arranged at a position displaced longitudinally from the centre of the holder 19, and, with the holder 19 held vertically with the stirrup 20 towards its lower end i. e. with the projection lowermost as shown in Fig. 5, the fuse cartridge 26 assumes defined position longitudinally when its upper end cap abuts the upper end face of the stirrup 20. The length of the stirrup 20 is considerably less than the length of the reduced diameter central portion of the fuse cartridge.

The end walls of the base 11 are notched. One end wall has a central notch 27 to accommodate the lower central projection 25 on the holder 19 and the other end wall has two spaced notches 28, 28, to accommodate the upper pair of projections 21, 21 on the holder 19.

The fuse cartridge and the holder 19 are presented to the base 11 in the vertical position already mentioned as shown diagrammatically in Fig. 7 and the end caps 26a of the fuse cartridge are forced into the spring contacts 12. In this position the holder 19 is not coextensive With the base 11 but is displaced in an upward direction therefrom, the position of the various projections being as indicated in Fig. 7. By sliding the holder 19 in downward direction, however, the cam surfaces of the two pairs of projections 21, 21 and 24, 24, on the face of the holder 19 come into engagement with the limbs of the spring contacts 12, and as the holder 19 is slid into the position where it is co-extensive with the base 11, the limbs of the contacts 12 are forced together by these cam surfaces, so as firmly to grip the fuse cartridge 26, thus providing good electrical contact and locking the fuse cartridge and holder in position on the base. The dimensions of the base and the holder are such that in this position a substantially dust-tight fuse is obtained, the holder just covering the open top of the base. During the sliding motion of the holder 19, of course, the fuse cartridge 26 remains substantially stationary within the spring contacts.

In Fig. 8 there is shown an alternative form of copper spring contacts 50, which may be employed in the base 11 in place of the contacts 12. As shown, the contact 59 is generally U-shaped, the limbs converging at 51 to form a neck and subsequently diverging and terminating in two wedge-shaped lips 52. The sides of the lips 52 converge so that, in use, when the holder 19 is inserted into the base 11 and displaced downwardly from the position illustrated in Fig. 7, the edges of the lips 52 of each contact present complementary engaging surfaces to the cam surfaces of the pairs of projections 21, 21 and 24, 24, so

that more efficient forcing-together of the limbs of the contacts 52 results. A tail 53 is provided for each contact, as also are projections 54 which serve to engage the notches 15 in the holder.

In Figs. 9, 10 and 11 similar reference numerals have been used for parts identical with those already described. In these figures, the holder 55 is slightly longer than the holder 19 shown in Figs. 4 to 6 so as to allow the provision of a stop 56 which is contiguous with the projection 25 against which the lower end cap 26a of the fuse cartridge 26 can rest. This arrangement avoids the necessity of the upper end cap of the fuse cartridge abutting the stirrup 57 as in the previous embodiment.

The stirrup 57 is of slightly different shape from that previously described, its inner faces diverging somewhat away from its arcuate portion so as to ensure firmer location of the fuse cartridge whilst still permitting passage of the end caps.

This embodiment of the fuse holder is assembled and employed with a base of corresponding dimensions in exactly the same manner as that previously described.

I claim:

1. An electric cartridge fuse of the type having a boxlike base with U-shaped spring contacts provided with lips and adapted to receive laterally end caps of a fuse cartridge held in a contactless holder of insulating material, said holder comprising a flat portion carrying a stirrup thereon, an aperture behind the stirrup, projections on either side of the stirrup which urge a reduced diameter portion of said cartridge against said stirrup, at least one pair of cam surfaces so positioned on said portion as to engage the lips of the spring contact.

2. An electric cartridge fuse of the type having a box like base with U-shaped spring contacts provided with wedge shaped lips and adapted to receive laterally end caps of a fuse cartridge held in a contactless holder of insulating material, said holder comprising a flat portion carrying a stirrup thereon, an aperture behind the stirrup, projections on either side of the stirrup which urge a reduced diameter portion of said cartridge against said stirrup, at least one pair of cam surfaces so positioned on said portion as to engage the lips of the spring contact and to present complementary engaging surfaces to the wedge shaped lips.

3. An electric cartridge fuse according to claim 1 wherein a stop is provided on the holder against which the cartridge is adapted to locate so as to define its longitudinal position upon insertion into the holder.

4. An electric cartridge fuse according to claim 1 wherein the lips on the spring contacts are wedge shaped and the cam surfaces present complementary engaging surfaces to the wedge shaped lips.

References Cited in the file of this patent UNITED STATES PATENTS 2,232,566 Shroyer Feb. 18, 1941 FOREIGN PATENTS 137,605 Australia June 15, 1950 543,486 France June 3, 1922 544,122 Great Britain Mar. 27, 1942 554,578 Great Britain July 9, 1943 

